Computers typically use an input device known as a "mouse" which determines the position of a pointer or cursor of a display screen. The mouse is guided over a flat surface in order to define a corresponding movement for the cursor on the screen. In operation, changes of x and y coordinates corresponding to movement of the mouse are sent to the computer by a cable or alternatively by an optical remote control. The computer calculates the position of the cursor or pointer on the screen and forms an image of the cursor at the defined position.
Known mouse cursor controls have the disadvantage of requiring space in addition to the space already occupied by the computer and the keyboard. Also, the required continuous back and forth movement of the hand between the keyboard and the mouse is not ergonomic.
For this reason, attempts have been made to integrate mouse-like units into a computer keyboard. For example, PCT Publication No. WO86/04166, published Jul. 17, 1986, U.S. Pat. No. 4,782,327, issued Nov. 1, 1988 to Kley et al., and U.S. Pat. No. 4,935,728 issued Jun. 19, 1990 to Kley disclose such a cursor control device. The disclosed device addresses many points within a distance of travel of a few centimeters. The precision required to position the cursor in this device is greater than can be easily achieved by the supplied manual cursor positioning device.
A cursor may be relatively precisely positioned if changes in the position of the cursor are addressed in a relative rather than an absolute manner. This can be achieved if the positioning element for the cursor has a defined zero position to which it automatically returns after a cursor position adjustment and from which the next relative position change of the cursor positioning element is started. The publication No. WO 86/04166 describes how such a positioning element can be mechanically pulled back to a zero or origin position by springs. In the disclosed device a positioning element is suspended by diagonal springs on the housing of an input unit. However, it is known from classical mechanics that elements coupled to springs are not returned to a precise zero or origin position, but oscillate about the zero position. Although this oscillation can be suppressed by damping or friction, if the friction or damping is too great the element is not consistently returned to the same zero point. Thus, in such a system the location of the zero rest position depends upon the initial conditions of the system, for example the initial direction and velocity of the positioning element when it is released. It is therefore desirable to provide a cursor positioning device which can be precisely reset to a zero point to allow relative cursor position addressing, without undesirable oscillations of the cursor position control. It is also desirable to provide such a mechanism which blocks the entry of dust or other debris into the cursor positioning mechanism.
It is an object of the invention to provide a movable cursor positioning element with a precise zero position from which it moves with reduced friction and with accuracy in response to an actuating force, the movement from the zero position being accurately represented by computer processed electrical signals. It is a further object to provide such a device which returns to its zero position in a consistent and precise manner, without oscillation, when the actuating force is removed.